CTL suppression induced by tumor cells in coculture assays is reversible. CTLs were cultured alone, with Meth A cells, or with purified normal B cells for three hours (A). After isolation of T cells by MACS, half of the CTLs were tested immediately in a 4-hour chromium release assay against EL-4 target cells. The remaining cells were cultured overnight with 5% IL-2 and tested in a similar chromium release assay (recovery). A similar 3-hour coculture assay was established to test whether or not CTL suppression induced by other tumors is reversible (B).